Single chip processor connected to an external memory chip

ABSTRACT

A digital processing system includes an external memory for the storage of program instructions for use with a separate processor that internally contains a memory for temporary storage, an arithmetic and logic means, a register set, control and timing circuitry, and two sets of data paths. The first set of data paths provide access to the external memory for transfer of instructions from the external memory to the processing unit. The second set of data paths provide for the internal routing of instructions data and addresses within the processor unit itself. The data structure for the first set of data paths is different than that for the second set of data paths, providing for an external data structure that is different than the internal data structure of the processor.

CROSS REFERENCE TO RELATED APPLICATION

This application is in the same subject area as application Ser. No. 279,879 filed July 2, 1981, also assigned to Texas Instruments.

BACKGROUND

1. Field of the Invention

This invention relates to computer memory interfaces, digital computers and electronic data processing systems.

2. Description of Prior Art

Digital processor systems ordinarily include a central processing unit with a memory. In microcomputer applications the program memory is contained on the same chip as the central processing unit. However, in larger microcomputer systems the program memory may be implemented on an external memory system set of chips and interfaced over an input/output line to the microcomputer chip containing the central processing unit. In digital processing systems requiring external memory, the interface between the memory chip and the central processing unit chip may be accomplished with either a hand shaking technique, i.e., the CPU chip sends a request over I/O line, then is answered by the memory chip over the same I/O line before the transfer is actually implemented, or the transfer could be synchronous, that is, the central processing unit requests memory access and then at a certain set time, reads the data that is available on the input/output lines from the external memory system. Using a synchronous interface to an external memory saves time and improves the performance of the microcomputer system. However, one must guarantee that the information from the external memory is available on the input/ouput data lines when the central processing unit chip expects to read the data. Problems arise when different external memory systems are used with the same microcomputer chip set since the external memory systems may and most probably do have different access time requirements. If the external memory system is faster than is required by the microprocessor system, then there is no problem if the external memory system can hold the data on the input/ouput lines until read. However, if the external memory system is slower than the microprocessor/microcomputer system, then errors may occur when the microcomputer or system attempts to read the data on the input/output bus since there is no guarantee that the data on the bus at the time it is read is the data that is being accessed from the external memory system. This invention solves the foregoing problem by providing an external memory interface for a microcomputer system that provides an automatic wait time to allow slower external memory systems to interface to the microcomputer system.

SUMMARY OF THE INVENTION

In accordance with the present invention, a digital processing system is provided that includes an external memory for storing instruction provided on several semiconductor substrates together with a processor unit fabricated on a separate semiconductor substrate and further including an internal memory for storage of data, an arithmetic and logic unit for performing the operations on the data, a set of registers for the temporary storage of data and addresses, a set of data paths which connect the internal memory to the arithmetic unit and the registers, a second data path which connects the external memory to the processor and control and timing circuitry for the production of control signals in response to the execution of instructions.

In one embodiment of this invention, a digital processing system is provided that has an external memory for the storage of all programs or instructions for the processor on a set of semiconductor chips that are separate from the processor unit which is on another semiconductor chip. The processor unit interfaces with the external memory through a data path or a data bus to input into the processor from the external memory the instructions. However, the data structure that is addressed by the processor in an external memory is different than the data structure internally within the processor. The data structure internally in the processor is made up of 16 bit words of 16 bit addresses. The data structure for the external memory is 16 bit addresses individually addressing 8 bit bytes. The processor provides for addressing these 8 bit bytes in external memory and forming a 2 byte word internally in the processor to form a complete instruction word for execution. In addition, internal memory is provided for the storage of instructions internally or the storage of data for execution of instructions internally. Any storage of instructions or data in the internal RAM, however, is temporary. This internal architecture provides for the equivalent of many internal working registers, allowing for a more efficient execution of the externally stored programs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a digital processing system including a processing unit interfaced to an external memory.

FIG. 2 is a memory map of the processing unit in FIG. 1.

FIG. 3 is a block diagram of the processing unit.

FIG. 4 is a flow chart illustrating the internal operations of the processing unit.

FIG. 5 is a diagram of the status register bit assignments.

FIG. 6 is a diagram of the workspace registers that are usable as index registers.

FIG. 7 is a diagram of the workspace pointer and registers.

FIG. 8 is a diagram of the signal interface between the processing unit and external memory.

FIG. 9 is a timing diagram of a memory read cycle for the external memory interface.

FIG. 10 is a timing diagram for the external memory WRITE cycle.

FIG. 11 is a timing diagram for the external memory interface Hold state.

FIG. 12 is a functional block diagram of the decrementor.

FIG. 13a is a timing diagram of the Wait state for external memory cycles showing the timing for a No-Wait state condition.

FIG. 13b is a timing diagram for the external memory showing one Wait state without any automatic first Wait state condition.

FIG. 13c is a timing diagram of the interface to an external memory showing an automatic Wait state.

FIG. 13d is a timing diagram for the communications register unit showing no Wait states.

FIG. 13e is a timing diagram for the communication register unit showing one Wait state.

FIG. 13f is a logic diagram showing the logic circuitry used to generate the automatic first Wait state condition.

FIG. 14a is a diagram of the external circuitry required to inhibit an automatic first Wait state.

FIG. 14b is a diagram of the external circuitry for inhibiting the automatic first Wait state using TTL speed reset request.

FIG. 14c is a diagram of the external circuitry for invoking the automatic first Wait state.

FIG. 15 is a diagram of the reset signal timing relationship for the processing unit.

FIG. 16 is a diagram of the non-maskable interrupt signal timing.

FIG. 17 is a functional diagram of the internal interrupt request latch.

FIG. 18 is a diagram of the interface signals to the communication register unit.

FIG. 19 is a diagram of the communication register address map.

FIG. 20 is a timing diagram for the communications register unit input cycle.

FIG. 21 is a timing diagram for the communications register unit output cycle.

FIG. 22 is a diagram illustrating the single bit communications register unit address development.

FIG. 23 is a diagram that illustrates the load communications register and store communication registers data transfers.

FIGS. 24a through 24n are illustrations of the individual instructions for the digital processing system of FIG. 1.

DESCRIPTIVE EMBODIMENT OF THE INVENTION

FIG. 1 represents a processing system including a processor 1, connected to an external memory 2. The interface between the processor 1 and external memory 2 is an address bus 12 that provides the address of data contained in the external memory 2, the data bus that allows the processor 1 to write into the external memory 2 or to read from the external memory 2 and seven control signals 14. The processor 1 includes a bus interface 3 that provides transmitting capabilities for the address bus and is connected to CPU 5 via line 6 in order to receive the address information from CPU 5. In addition, bus interface 3 receives data information from CPU 5 via line 7 and transmits or receives this information to the external memory 2 via the data bus 13. Bus control 4 is interfaced to CPU 5 through lines 9 and 8. Lines 9 provides the outgoing control to the external memory 2. Line 8 provides the external memory ready signal to the CPU 5. The reset signal used to initialize the CPU is also inputted into both the bus control 4 and the CPU 5 via lines 11 and 10. The reset signal is used to initialize the CPU 5 and also to define the auto wait state condition in the bus control 4.

FIG. 2 illustrates the memory map for processor 1. Shown are the locations in the memory address space for the reset signal, a nonmaskable interrupt signal, other interrupts and the XOP trap vectors, and a dedicated address segments for the on-chip RAM and the on-chip memory mapped input/output. An XOP is a software interrupt.

The block diagram of the Processor 1 is shown in FIG. 3. A flow chart, representative of the Processor 1 functional operation, is shown in FIG. 4.

Arithmetic Logic Unit

The artichmetic logic unit (ALU) 52 is the computational component of the Processor 1. It performs all arithmetic and logic functions required to execute instructions. The functions include addition, substraction, AND, OR, exclusive OR, and complement. The ALU 52 is arranged in two 8-bit halves to accommodate byte operations. Each half of the ALU 52 operates on one byte of the operand. During word operand operations, both halves of the ALU 52 function in conjunction with each other. However, during byte operand processing, results from the least significant half of the ALU 52 are ignored. The most significant half of the ALU 52 performs all operations on byte operands so that the status circuitry used in word operations is also used in byte operations.

Internal Registers

The following three (3) internal registers are accessible to the user (programmer):

Program Counter (PC) 47

Status Register (ST) 46

Workspace Pointer (WP) 48

Program Counter

The program counter (PC) 47 is a 15-bit counter that contains the word address of the next instruction following the instruction currently executing. The pocessor 1 references this address to fetch the next instruction from memory and increments the address in the PC 47 when the new instruction is executing. If the current instruction in the processor 2 alters the contents of PC 47, then a program branch occurs to the location specified by the altered contents of PC 47. All context switching operations plus simple branch and jump instructions affect the contents of PC 47.

Status Register

The status register (ST) 46 is a fully implemented 16-bit register that reports the results of program comparisons, indicates program status conditions, and supplies the arithmetic overflow enable and interrupt mask level to the interrupt priority circuits. Each bit position in the register signifies a particular function or condition that exists in the processor. FIG. 5 illustrates the bit position assignments. Some instructions use the status register 46 to check for a prerequisite condition; others affect the values of the bits in the register; and others load the entire status register with a new set of parameters. Interrupts also modify the status register 46.

Workspace

The processor 1 uses blocks of memory words called workspaces for instruction operand manipulation. A workspace occupies 16 contiguous words in any part of memory that is not reserved for other use. The individual workspace registers may contain data or address, or function as operand registers, accumulators, address registers, or index registers. Some workspace registers take on special significance during execution of certain instructions. Table 1 lists each of these dedicated workspace registers and the instructions that use them. FIG. 6 defines the workspace registers that are allowed to be used as index registers.

Workspace Pointer

To locate the workspace in memory, a hardware register called the workspace pointer (WP) 48 is used. The workspace pointer 48 is a 16-bit register that contains the memory address of the first word in the workspace. The address is left-justified with the 16th bit (LSB) hardwired to logic zero. The processor 1 accesses each register in the workspace by adding twice the register number to the contents of the workspace pointer 48 and initiating a memory request for that word. FIG. 7 illustrates the relationship between the workspace pointer and its corresponding workspace in memory. It should be noted that the Processor 1 adds the workspace pointer (WP) 48 to twice the register number to derive actual register addresses. For instructions performing byte operations, use of the workspace register addressing mode will result in the most significant byte of the workspace register 48 involved to be used as the operand for the operation. Since the workspace is also addressable as a memory address, the least significant byte may be directly addressed using any one of the general memory addressing modes.

Context Switching

The workspace concept is particularly valuable during operations that require a context switch, which is a change from one program environment to another, as in the case of a subroutine or an interrupt service routine. Such an operation using a conventional multi-register arrangement requires that at least part of the contents of the register file be stored and reloaded using a memory cycle to store or fetch each word. The processor 1 accomplishes this operation by changing the workspace pointer 48. A context switch requires only three store cycles and two fetch cycles, exchanging the program counter 47, status register 46 and workspace pointer 48. After the switch, the workspace point 48 contains the starting address of a new 16-word workspace in memory for use in the new routine. A corresponding time saving occurs when the original context is restored. Instructions in the processor 1 that result in a context switch include: Call subroutine (BLWP), Return from Subroutine (RTWP) and the Extended Operation (XOP) instruction. All interrupts also cause a context switch by forcing the processor 1 to trap to a service subroutine.

External Memory Interface

The signals used in the processor interface to external memory 2 are shown in FIG. 8. IAQ/HOLDA and HOLD- are not required for simple memory systems, but will be used by DMA controllers.

Memory Read Operations

To perform a memory read operation, the processor 1 first outputs the appropriate address on A0-A14 and A15/CRUOUT, and asserts MEMEN. The processor 1 then places its data bus drivers in the high impedance state, asserts DBIN, and then reads in the data byte. Completion of the memory read cycle and/or generation of Wait states is determined by the READY input. Timing relationships of the memory read sequence are shown in FIG. 9. Note that MEMEN remains active (low) between consecutive memory operations.

Although not explicitly shown in FIG. 9, reading a word (two 8-bit bytes) from external memory requires two memory read cycles that occur back-to-back (a Hold state request will not be granted between cycles). If an instruction directs that a byte read operation from external memory is to be performed, only the byte specifically addressed will be read (one memory read cycle). External words are accessed most-significant (even) byte first, followed by the least-significant (odd) byte. A valid address is present on the A0 to A7, A15/CRUOUT address bus at 100. The processor 1 then awaits the data transmission from external memory 2 which is illustrated at 102. The data at 102 must be valid at the fall of the CLKOUT edge. IAQ/HOLDA (103 in FIG. 9) will only be asserted during memory read cycles if an instruction OP code is being read. During memory read cycles in which an instruction opcode is being read. IAQ/HOLDA is asserted as shown in FIG. 9. Note that since an instruction opcode is a word in length, IAQ/HOLDA remains asserted between the two byte read operations involved when an instruction opcode is read from the external memory address space.

Memory Write Operations

To perform a memory write operation, the processor 1 first outputs the appropriate address on A0-A14 and A15/CRUOUT, and asserts MEMEN. The processor 1 then outputs the data byte being written to memory on pins D0 through D7, and then asserts WE-/CRUCLK-. Completion of the memory write cycle and/or generation of Wait states is determined by the Ready input. Timing relationships of the memory write sequence are shown in FIG. 10. A valid address is present at 110 on the A0-A14, A15/CRUOUT address bus. On the data bus D0 through D7, valid memory write data is present at 111. Note that IAQ/HOLDA (112 in FIG. 10) will never be asserted during a memory cycle. Note that MEMEN remains active (low) between consecutive memory operations. Writing a word (two 8-bit bytes) to the external memory 2 requires two memory write cycles that occur back-to-back. (A Hold state request will not be granted between cycles.). In an instruction directs that a byte write to external memory 2 is to be performed, only the byte specifically addressed will be written (one memory write cycle). External words are accessed most-significant (even) byte first followed by the least-significant (odd) byte.

Direct Memory Access

The processor 1 Hold state allows both external devices and the processor 1 to share a common external memory. To gain direct memory access (DMA) to the common memory, the external device first requests the processor to enter a Hold state by asserting (taking low) the HOLD input. The processor 1 will then enter a Hold state following completion of the cycle (either memory, CRU, external instruction, or internal ALU cyucles) that it is currently performing. Note, however, that a Hold state is not entered between the first and second byte accesses of a full word in the external memory address space, and a Hold state is not entered between the first and second clock cycles of a CRU cycle.

Upon entering of a Hold state, the processor 1 puts its address, data, DBIN, and WE/CRUCLK drivers in the high impedance mode, and asserts IAQ/HOLDA. The external device can then utilize these signal lines to communicate with the common memory. After the external device has completed its memory transactions, it releases HOLD, and the processor 1 continues instruction execution at the point where it had been suspended. Timing relationships for this sequence are shown in FIG. 11.

To all DMA loading of external memory on power-up, the processor 1 does not begin instruction execution after a Reset state until HOLD has been removed if HOLD was active (low) at the time RESET was taken from low to high RESET released.

External devices cannot access the internl (on-chip) memory address space of the processor 1 when it is in the Hold state.

Since IAQ (Instruction Opcode Acquisition) and HOLDA (Hold Acknowledge) are multiplexed on a single signal, IAQ/HOLDA, this signal must be gated with MEMEN using external logic to separate IAQ and HOLDA. When MEMEN=0,1AQ/HOLDA can indicate IAQ and when MEMEN=1, 1AQ/HOLDA can indicate HOLDA.

Internal Memory Address Space

Access of the internal (on-chip) memory address space (to access the internal RAM 45 and decrementer 51) is transparent to the processor 1 instruction set. That is, operands can be read from and written into locations in the internal memory 45 space simply by using the appropriate addresses via any of the addressing modes in the processor 1 instruction set, and instructions can even be executed from the internal memory space by loading the appropriate address into the program counter 47 of the processor 1.

The processor 1 indicates to the external world when these internal memory address space accesses are occurring by asserting the same signals used for accessing external memory 2 (see FIG. 8) in a manner very similar to an external memory 2 address space access. There are a few differenes in these cycles, however, and these differences are detailed in the following paragraphs.

When performing an internal memory address space access, the processor 1 outputs the same signals that it would for an external memory space access, with the same timing (see FIGS. 9 and 10) except for the following:

(1) A single cycle (read or write) is outputted as both internal bytes are accessed simultaneously. Externally, it appears as though a single byte memory access cycle to an internal address is occurring.)

(2) The cycle always has no Wait states, and the READY input is ignored by the processor 1.

(3) During read cycles, the data bus (D0-D7) output drivers are put in the high-impedance mode. During write cycles, the data bus outputs non-specific data.

During read cycles to the internal memory address space, the processor 1 does not make the read data available to the external world. If an instruction is executed from the internal memory address space, IAQ/HOLDA is still asserted, but only during the one read cycle shown externally while the full word is read internally.

When a Hold state, external devices are not able to access the internal memory address space.

Internal RAM

The 256 bytes of internal random-access read/write memory 45 (RAM) are organized internally as 128 16-bit words. Since the processor 1 has 16-bit internal data paths, two 8-bit bytes are accessed each time a memory access is made to the internal RAM 45.

Byte accesses are transparent to the internal RAM 45. That is, when an instruction addresses a byte in the internal RAM 45, the processor 1 will: (1) read the entire word but only use the byte specifically addressed for a read operation and, (2) only write to the specifically addressed byte and not alter the contents of the other byte in the word during a write operation.

Decrementer (Timer/Event Counter)

Accessible via one of the word addresses (see FIG. 2) of the internal memory-mapped I/O address space is the decrementer 51. The on-chip decrementer logic can function as a programmable read-time clock, an event timer, or as an external event counter. A block diagram of the decrementer that is representative of its functional operation is shown in FIG. 12. Note that Flag 0 and Flag 2 are bits of the Flag Register 53. The decrementer 51 is configured as either a timer or an event counter using bit FLAG0 of the internal Flag register 53. The decrementer 51 is enabled/disabled using bit FLAG1 of the internal Flag register 53. The FLAG0 is set to zero, the decrementer 51 will function as a timer. When FLAG0 is set to one, the decrementer 51 will function as an event counter. When FLAG 1 is set to zero, the decrementer 51 is disabled and will not be allowed to decrement and request level 3 interrupt traps. When FLAG1 is set to one, the decrementer 51 is enabled and will decrement and request level 3 interrupt traps. It should be noted that when the decrementer 51 is configured as a timer, INT4/EC will be usable as an external interrupt level 4 trap request. When the decrementer 51 is configured as an event counter, INT4/EC is the input for the "event counter" pulses, and an interrupt level 4 trap request input is no longer available externally or internally.

The general operation of the decrementer 51 is as follows. FLAG0 of the Flag register 53 is first set to select the desired mode of operation. The desired start count is then loaded into the Starting Count Storage Register 120 by performing a memory write of the count word to the dedicated internal memory mapped I/O address of the decrementer 51. (This also loads the Decrementing Register with the same count 121.) The decrementer 51 is then enabled and allowed to start decrementing by setting FLAG1 of the Flag Register 53 to one. Both FLAG0 and FLAG1 are set to zero when the processor 1 is reset. When the count in the Decrementing Register 121 reaches zero, the level 3 internal interrupt request latch 122 is set, the Decrementing Register 121 is reloaded from the Starting Count Storage Register 120, and decrementing continues. Note that writing a start count of 0000₁₆ to the decrementer 51 will disable it.

When configured as a timer, the decrementer 51 functions as a programmable read-time clock by decreasing the count in the Decrementing Register 121 by one for each fourth CLKOUT cycle. Loading the decrementer 51 with the appropriate start count causes an interrupt to be requested every time the count in the Decrementing Register 121 reaches zero. The decrementer 51 can also be used as an event timer when configured as a timer by reading the decrementer 51 (which is accomplished by performing a memory read from the dedicated internal memory mapped I/O address of the decrementer) at the start and stop points of the event of interest and comparing the two values. the difference will be a measurement of the elapsed time.

When configured as an event counter, operation is as previously discussed except that each high-to-low transition on INT4/EC will cause the decrementing Register 121 to decrement. These INT4/EC high-to-low transitions can be asynchronous with respect to CLKOUT. Note that INT4/EC can function as a negative edge-triggered interrupt by loading a start count of one.

The decrementer 51 should always be accessed as a full word (two 8-bit bytes). Reading a byte from the decrementer does not present a problem since only the byte specifically addressed will be read. Writing a single byte to either of the bytes of the decrementer will result in the data byte being written into the byte specifically addressed and random its being written into the other byte of the decrementer 51.

Wait State Generation

Wait states can be generated for external memory cycles, external CRU cycles and external instruction cycles for the processor 1 using the READY input. A Wait state is defined as extension of the present cycle by one CLKOUT cycle. The timing relationships of the READY input to the memory interface and the CRU interface signals are shown in FIG. 13. Note that Wait states cannot be generated for memory cycles that access the internal memory address space or for CRU cycles that access the internal CRU address space, as the READY input will be ignored during these cycles.

In FIG. 13a, the contents of the data bus is inputted into the internal registers at point 125 since the READY line is high. In FIG. 13b, there is an attempted read at point 126 but since the READY line is low, there is one wait state. The data is then read in in point 127 at the fall of the next clock since the READY line is high at that time. Note that in both figures 13a and b there is not an automatic wait state condition present. In FIG. 13c, the automatic wait state condition is present and no access is attempted at time 128. However, at 129 when the ready line is high, the data bus is read. FIGS. 13d and 13e refer to the communications register unit interface. Note that at time 130 when the READY line is high, there is an access. In FIG. 13e at point 131 since the READY line is low, there will be no access but the access will wait until the second clock edge at 132. Note that the automatic first wait state condition does not apply to CRU cycles.

The Automatic First Wait State Generation feature of the processor 1 allows a Wait state to be inserted in each external memory cycle, regardless of the READY input, as shown in FIG. 13. The Automatic First Wait State Generation feature can be involved when RESET is asserted. If READY is active (high) when RESET goes through a low-to-high transition, the first Wait state in each external memory cycle will be automatically generated. If READY is inactive (low) when RESET goes through a low-to-high transition, no Wait state will be inserted automatically in each external memory cycle. There is a one and one-half CLKOUT cycle time minimum setup time requirement on READY before the reset low-to-high transition. The recommended external circuitry for invoking or inhibiting the Automatic First Wait State Generation feature is shown in FIG. 14. Note that this feature does not apply to internal memory address space accesses, external instruction cycles, or any CRU cycles. Wait states cannot be generated during internal ALU/other operation cycles. The READY input is ignored during these cycles.

A circuit for providing the wait state is shown in FIG. 13f. Block 15 contains the circuitry that will determine if an automatic wait state condition is required in the operation of the processor 1. The contents of block 15 are illustrated in FIGS. 14A, B and C. Block 15 receives as inputs the READY line and the RESET line on line 11. The output of block 15 are lines 17 which represents the READY line and line 16 which is the RESET signal. Line 17 and 16 are inputted into block 18 which is a SR type flip flop. The RESET signal on line 16 is used to clock the flip flop as shown. The READY signal on line 17 is used to set the flip flop. The output of this flip flop determines whether or not the auto wait state condition is required. If the condition is required, then the ready line will be high at the rising edge of RESET; thus clocking the flip flop 18 and inputting a 1 into the S terminal causing a 1 to be present on the Q terminal of flip flop 18. Therefore, line 22 will be high to indicate the auto wait state condition being present. Located below the flip flop 18 is OR gate 24 which receives a read line input 25 and the write line 26. The output of the OR gate 24, line 29, is high when either a memory read or memory write operation is being performed. This provides an input into AND gate 27 and AND gate 31. Referring now to AND gate 31, the ready line inputs a signal into AND gate 31 via line 17, line 19 and line 20. AND gate 31 also receives an input from the read/write OR gate 24 via line 28 and 21. The AND gate 31 further receives the output of flip flop 18 via line 22 which is inverted in inverter 43. AND gate 31 produces a high output of line 37 when the READY line is high, when there is a READ/WRITE operation and when the AUTO/WAIT state condition is not selected. AND gate 27 is used to start the auto wait state process. AND gate 27 receives an input from flip flop 18 from line 22 and line 23 to indicate the selection of the auto wait state condition. In addition to receiving the output over line 29 from the read/write OR gate 24. AND gate 27 produces a high output on line 30 when the auto wait state condition has been selected and a read/write sequence has begun. Line 30 is used as an input to flip flop 34 which receives an additional input 32 from the central processing unit internal clock. Flip flop 34 produces an output level on line 35 when the clock signal on line 32 goes high and the output from AND gate 27 is high on line 30. This output is ANDed in AND gate 36 with line 19 which is the READY signal from the external memory 2. The output of AND gate 36 is ORed with line 37 from AND 31 as previously discussed. When either one of these are high, OR gate 38 places a high output signal into flip flop 41 via line 44. Flip flop 41 is clocked by line 39 which is the internal clock that also clocks flip flop 34 on line 32. The output of flip flop 41 is a high output on line 42 which signifies the transfer of the contents of the data bus to the internal registers within processor 1. It should be noted that lines 33 and 40 which provide clear signals to the flip flops, 34 and 41, respectively, are provided by the processor to clear these flip flops after a reading of the data line.

Processor Interrupts

The processor 1 implements seven prioritized, vectored interrupts, some of which are dedicated to predefined functions and the remaining are user-definable. Table 2 defines the source (internal or external), assignment, priority level, trap vector location in memory, and enabling/resulting status register interrupt mask values for each interrupt.

The processor 1 will grant interrupt requests only between instructions (except for Level 0 Reset), which will be granted whenever it is requested, i.e., in the middle of an instruction). The processor 1 performs additional functions for certain interrupts, and these functions will be detailed in subsequent sections. The basic sequence that the processor 1 performs to service all interrupt requests is as follows:

(1) Prioritize all pending requests and grant the request for the highest priority interrupt that is not masked by the current value of the interrupt mask in the status reguster 46 or the instruction that has just been executed.

(2) Make a context switch using the trap vector specified for the interrupt being granted.

(3) Reset ST7 through ST11 in the status register 46 to zero, and change the interrupt mask (ST12 through ST15) as appropriate for the level of the interrupt being granted.

(4) Resume execution with the instruction located at the new address contained in the PC 47, and using the new WP 48. All interrupts will be disabled until after this first instruction is executed, unless: (a) RESET is requested, in which case it will be granted, or (b) the interrupt being granted is the MID request and the NMI interrupt is requested simultaneously (in which case the NMI request will be granted before the first instruction indicated by the MID trap vector is executed.)

This sequence has several important characteristics. First, of all, for those interrupts that are maskable with the interrupt mask in the status register, the mask will be changed to a value that will permit only interrupts of higher priority to interrupt their service routines. Secondly, status bit ST10 (overflow interrupt enable) is reset by zero by the servicing of any interrupt so that overflow interrupt requests cannot be generated by an unrelated program segment. Thirdly, the disabling of other interrupts until after the first instruction of the service routine is executed permits the routine to disable other interrupts by changing the interrupt mask with the first instruction. Lastly, the vectoring and prioritizing scheme of the processor 1 permits interrupts to be automatically nested in most cases. If a higher priority interrupt occurs while in an interrupt service routine, a second context switch occurs to service the higher priority interrupt. When that routine is complete, a return instruction (RTWP) restores the saved context to complete processing of the lower priority interrupt. Interrupt routines should, therefore, terminate with the return instruction to restore original program parameters.

External Interrupt Requests

Each of these interupts is requested when the designated signal is supplied to the processor 1.

Interrupt Level 0 RESET

Interrupt Level 0 is dedicated to the RESET input of the processor. When active (low), RESET causes the processor to stop instruction execution and to inhibit (take to logic level high) MEMEN, DBIN, and WERUCLK/ . The processor 1 will remain in the Reset state as long as RESET is active.

When RESET is released (low-to-high transition), the processor 1 performs a context switch with the Level 0 interrupt trap vector (WP and PC of trap vector are in memory word addresses 0000₁₆ and 0002₁₆, respectively.) Note that the old WP, PC and ST are stored in workspace registers 13, 14, and 15 of the new workspace. The processor 1 then resets all status register bits, the internal interrupt request latches, Flag Register bits FLAG0 and FLAG1 and the MID Flag. After this, the processor 1 starts execution with the new PC 47.

If HOLDA is active (high) due to HOLD being active (low) when RESET becomes active, RESET will cause HOLDA to be released (taken low) at the same time as MEMEN, DBIN, and WERUCLK/ are taken inactive (high). HOLD can remain active as long as RESETis active and HOLDA will not be asserted. If HOLD is active and the processor 1 will remain in this hold state until HOLD is released. This RESET and HOLD priority scheme facilitates DMA loading of external RAM upon power-up.

Timing relationships of the RESET signal are shown in FIG. 15. Note that don't cares 140 indicate that any type of processor cycle can be taking place. At 150 RESET is sampled at every high-to-low CLKOUT transition. At point 151 RESET is required to be active low for a minimum of two samples to initiate the sequence. The context switch would begin one CLKOUT cycle after 151 if RESET were active high at 151. At point 152, the context switch using the RESET trap vector begins one CLKOUT cycle after RESET is sampled as having returned to the inactive high level.

Release of the RESET signal is also the time at which the Automatic First Wait State function of the processor 1 can be invoked.

Non-Maskable Interrupt (NMI)

The NMI signal is the request input for the NMI level interrupt and allows ROM loaders single-step/breakpoint/maintenpanel functions, or other user-defined functions to be implemented for the processor 1. NMI being active (low) according to the timing illustrated in FIG. 16 constitutes a request for the NMI level interrupt. Note at point 155 NMI is sampled every high to low CLKOUT transition. To be recognized, NMI must be active low at the end of an instruction. Since instructions are variable in length, the minimum active time for NMI is variable according to the instruction being executed. Point 153 illustrates the last possible time that NMI must be recognized at or before execution of the next instruction. The NMI context which begins 3 CLKOUT cycles after execution of the current instruction is complete. At points 156, after an NMI context switch sequence has been initiated, NMI can remain active low indefinitely without causing consecutive NMI trap requests. To enable another NMItrap request, NMI must be taken inactive high and be sampled at least once at the inactive level. The processor 1 services this request exactly according to he basic sequence previously described, with the priority level, trap vector location, and enabling/resulting status register interrupt mask values as defined in Table 2. Note that the processor 1 will always grant a request for the NMI level interrupt immediately after execution of the currently executing instruction is completed since NMI is exempt from the interrupt-disabling-after-execution characteristic of certain instructions and also the current value of the interrupt mask.

It should also be noted that the processor 1 implements four bytes of its internal RAM 45 at the memory address of the NMI vector. This allows usage of the NMI level in minimum-chip processor 1 systems. It also requires, however, that this vector must be initialized, upon power-up, before the NMI level interrupt can be requested.

Interrupt Levels 1 and 4 (INT1 and INT4/EC)

The INT1 and INT4/EC signals are the request inputs for the Level 1 and Level 4 interrupts, respectively. (Note that if the decrementer is configured as an event counter, INT4/EC is no longer a Level 4 interrupt request input. levels 1 and 4 are maskable, user-definable interrupts.

The INT1 and INT4-/EC interrupt inputs can accept either asynchronous pluses or asynchronous levels as input signals. An internal interrupt request latch stores the occurrence of a pulse. A block diagram of the processor 1 internal logic for these request latches that is representative of their functional operation is shown in FIG. 17. Note at point 158 a separate latch and synchronizer is implemented for level (INT1) and level 4 (INT4-/EC). For level 1 the input shown here is directly from the INT1 pin. For level 4 the input shown is from the gating shown in FIG. 12. Note that with this implementation only a single interrupt source is allowed if the input signal is a pulse, but multiple interrupt sources can be wired-Ored together provided that each source supplies a level as the input signal. (The levels are then removed one at a time by a hardware/software mechanism activated by the interrupt subroutine as each interrupting source is serviced by the subroutine.)

The processor 1 services each of these requests exactly according to the basic sequence previously described with the priority levels, trap vector locations, and enabling/resulting status register interrupt mask values as defined in Table 2. Each internal interrupt request latch will get reset when the context switch for its associated interrupt level occurs.

Internally Generated Interrupts

Each of these interrupts is requested when the designated condition has occurred in the processor 1.

Macro Instruction Detection (MID) Interrupt

The acquisition and attempted execuion of an MID interrupt opcode will cause the MID level interrupt to be requested before execution of the next instruction begins. In addition to requesting the MID level interrupt, the MID flag is set to one "1". The processor 1 services this request exactly according to the basic sequence previously described, with the priority level, trap vector location, and enabling/resulting status register interrupt mask values as defined in Table 2. Note that the processor 1 will always grant a request for the MID level interrupt since MID is not affected by the interrupt mask and is higher in priority than any other interrupt except for Level 0, Reset. If the NMI interrupt is requested during an MID interrupt context switch, the MID interrupt context switch will be immediately followed by the NMI interrupt service sequence before the first instruction indicated by the MID interrupt is executed. This is done so that the NMI interrupt can be used for a single-step function with MID opcodes. Servicing the MID interrupt request is viewed as "execution" of an MID interrupt opcode. NMI allows the processor 1 to be halted immediately after encountering an MID opcode.

It should also be noted that the MID interrupt shares its trap vector with Level 2, the Arithmetic Overflow interrupt. The interrupt subroutine beginning with the PC of this vector should examine the MID Flag to determine the cause of the interrupt. If the MID Flag is set to "1", an MID interrupt has occurred, and if the MID Flag is set to "0", an Arithmetic Overflow interrupt has occurred. The portion of this interrupt subroutine that handles MID interrupts should always, before returning from the subroutine, reset the MID Flag to "0".

The MID interrupt has basically two applications. The MID opcodes can be considered to be illegal opcodes. The MID interrupt is then used to detect errors of this nature. The second and primary application of the MID interrupt, is to allow the definition of additional instructions for the processor 1. MID opcodes are used as the opcodes for these macro instructions. Software in the MID interrupt service routine emulates the execution of these instructions. The benefit of this implementation of macros is that the macro instructions can be implemented in microcode in future processors and software will then be directly transportable to these future processors.

Note that the processor 1 interrupt request processing sequence does create some difficulties for re-entrant usage of MID interrupt macro instructions. In general, to avoid possible errors, MID interrupt macro instructions should not be used in the NMI and Level 1 interrupt subroutines, and should only be used in the Reset subroutine if Reset is a complete initialization of the system.

Arithmetic Overflow Interrupt

The occurrence of an arithmetic overflow condition, defined as status register 46 bit 4 (ST4) getting set to one can cause the Level 2 interrupt to be requested. Note that this request will e granted immediately after the instruction that caused the overflow condition. The processor 1 services this request exactly according to the basic sequence previously described with the priority level, trap vector location, and enabling/resulting status register interrupt mask values as defined in Table 2.

In addition to being maskable with the interrupt mask, the Level 2 overflow interrupt request is enabled/disabled by status register bit 46 10 (ST10), the Arithmetic Overflow Enable Bit (i.e., ST10=1 enables overflow interrupt request; ST10=0 disables overflow interrupt request). if servicing the overflow interrupt request is temporarily overridden by servicing of a high priority interrupt, the occurrence of the overflow condition will be retained in the contents of the status register 46, i.e., ST4=1, which is saved by the higher priority context switch. Returning from the higher priority interrupt subroutine via an RTWP instruction causes the overflow condition to be reloaded into status register 46 bit ST4 and the overflow interrupt to be requested again (upon completion of RTWP instruction). The arithmetic overflow interrupt subroutine must reset ST4 or ST10 to zero in the status word saved in workspace register 15 before the routine is completed to prevent generating another overflow interrupt immediately after the return.

It should also be noted that the Level 2 arithmetic overflow interrupt shares its trap vector with the MID interrupt.

Decrementer Interrupt

The occurrence of an interrupt request by the decrementer will cause the Level 3 internal interrupt request latch to get set. This latch is similar to those for Levels 1 and 4 in that it is reset by servicing a Reset interrupt or when the context switch for its associated interrupt level occurs (FIG. 17).

The Level 3 internal interrupt request latch being set constitutes a request for a Level 3 interrupt, and the processor 1 services this request exactly according to the basic sequence previously described with the priority level, trap vector location, and enabling/resulting status register interrupt mask values as defined in Table 2.

Communication Register Unit interface

The processor 1 accomplishes bit I/O of varying field width through the use of the Communications Register Unit (CRU). In applications demanding a bit-oriented I/O interface, the CRU performs its most valuable act: transferring a specified number of bits to or from memory and a designated device. Thus, the CRU is simply a linking mechanism between memory and peripherals.

Acting as a shift register, the CRU is a separate hardware structure of the processor 1. This structure can serially transfer up to 16 bits of data between the CRU and a specified device in a single operation. The 32768-bit CRU address space may be divided into any combination of devices, each containing any number of input or output bits. When given the bit address of a device, the CRU can test or modify any bit in that unit. Several consecutive addresses can be occupied by a device. These CRU applications are controlled by single and multiple-bit instructions.

Single-bit instructions facilitate the testing or modification particular bit in a device. The device in which a bit is to be tested (TB), set to zero (SBZ), or set to one (SBO) is designated by the sum of the value workspace in workspace Register R12 and an 8-bit signed displacement value included as an operand of that instruction.

Multiple-bit instructions control the serial transfer of up to 16 bits between memory and peripherals. The device with which communication is to take place is addressed by workspace Register R12. The memory address to or from which data is to be transferred, as well as the number of bits to be transferred are included as operands of the multiple-bit instruction.

The signals used in the processor 1 interface to the CRU are shown in FIG. 18. The CRU address map is shown in FIG. 19.

The concept of "CRU space" is the key to CRU operations. An ideological area exists in which peripheral devices reside in the form of an address. The CRU space is this ideological area; it has monotonically increasing bit addresses. Each bit represents a bistable I/O point which can be read from or written to. CRU address space and memory address space are independent of each other. Memory space is byte-addressable and CRU space is bit-addressable. Therefore, a desired device is accessed by placing its software base address in workspace Register R12 and exercising the CRU commands.

CRU nomenclature is built around the four address types involved in its operation. The software base address, hardware base address, address displacement, and CRU bit address interact to link memory to peripherals in bit-serial communication via the CRU.

The software base address consists of the entire 16 bits of workspace register R12. In workspace register R12, the programmer loads twice the value of the CRU hardware address of the device with which he wishes to communicate. Because only bit 0 through 14 of workspace register R12 are placed on the address bus, the programmer need to shift the hardware base address left one position.

Bit 0 through 14 of workspace Register R12 form the hardware base address. For the single-bit instructions, the hardware base address is added to the address displacement to obain the CRU bit address. For multiple-bit instructions the hardware base address is the CRU bit address.

External CRU Devices

To input a data bit from an external (off-chip) CRU device, the processor 1 first outputs the appropriate address on A0-A14. The processor 1 leaves MEMEN-high, outputs logic zeros on D0-D2, strobes DBIN-, and reads in the data bit on CRUIN. Completion of each CRU input cycle and/or generation of Wait states is determined by the READY input. Timing relationships of the CRU input cycle are shown in FIG. 20. Note at point 160, the address is valid. At 161 D0-D2 each output a logic 0. At 163 there is a nonspecific output bit. At 164 the CRU input bit must be valid on CRUIN at the CLKOUT edge indicated.

To output a data bit to an external (off-chip) CRU device, the processor 1 first outputs the appropriate address on A0-A14. The processor 1 leaves MEMEN-high, outputs logic zeros on D0-D2, outputs the data bit on A15/CRUOUT, and strobes WE-/CRUCLK-. Completion of each CRU output cycle and/or generation of Wait states is determined by the READY input. Timing relationships of the CRU output cycle are shown in FIG. 21. At point 171, the address is valid. At point 172, D0-D2 lines output logic is "0". At point 173 there is a valid CRU output bit for the address being output. Point 174 represents don't care conditions.

For multiple-bit transfers, these input and output cycles are repeated until transfer of the entire field of data bits specified by the CRU instruction being executed has been accomplished.

Single-Bit CRU Operations

The processor 1 performs three single-bit CRU functions: Test Bit (TB), Set Bit to One (SBO), and Set Bit to Zero (SBZ). The SBO instruction performs a CRU output cycle with logic one for the data bit, and the SBZ instruction performs a CRU output cycle with logic zero for the data bit. A TB instruction transfers the addressed CRU bit from the CRUIN input line to bit 2 of the status register (bit ST2, the EQUAL bit).

The processor 1 develops a CRU bit address for the single-bit operations from the CRU base address contained in workspace register R12 and the signed displacement count contained in bits 8 through 15 of the instruction. The displacement allows two's complement addressing from base minus 128 bits through base plus 127 bits. The base address from workspace Register R12 is added to the signed displacement specified in the instruction and the result is placed onto the address bus. FIG. 22 illustrates the development of a single-but CRU address.

Multiple Bit CRU Operations

The processor 1 performs two multiple-bit CRU operations: store communications register (STCR) and load communications register (LDCR). Both operations perform a data transfer from the CRU-to-memory or from memory-to-CRU as illustrated in FIG. 23. Although the figure illustrates a full 16-bit transfer operation, any number of bits from 1 through 16 may be involved.

The LDCR instruction fetches a word from memory and right shifts it to serially transfer it to CRU output bits. If the LDCR involves eight or fewer bits, those bits come from the right-justified field within the addressed byte of the memory word. If the LDCR involves nine or more bits, those bits come from the right-justified field within the whole memory word. Workspace register R12, bits 0 through 14, defines the starting bit address. When transferred to the CRU interface, each successive bit receives an address that is sequentially greater than the address fro the previous bit. This addressing mechanism results in an order reversal of the bits; that is, bit 15 of the memory word (or bit 7) becomes the lowest addressed bit in the CRU and bit 0 becomes the highest bit in the CRU field.

A STCR instruction transfers data from the CRU to memory. If the operation involves a byte or less transfer, the transferred data will be stored right-justified in the memory byte with leading bits set to zero. If the operation involves from nine to 16 bits, the transferred data is stored right-justified in the memory word with leading bits set to zero. When the input from the CRU device is complete, the lowest addressed bit from the CRU is in the least significant bit position in the memory word or byte.

Internal CRU Devices

Access of internal (on-chip) CRU devices is transparent to the processor CRU instructions. Data can be input from and output of the bits of the internal CRU devices simply by using the appropriate CRU addresses to access these bits.

The processor 1 will indicate to the external world when the internal CRU bit accesses are occurring by asserting the same signals used for accessing external CRU devices (see FIG. 18). the timing of these signals for internal CRU input and output cycles will be identical to the timing for external CRU input and output cycles (see FIGS. 20 and 21) except that during internal CRU cycles, the READY input is ignored, i.e., Wait states cannot be generated, and, during internal CRU input cycles, the processor 1 will ignore the CRUIN input signal. The internal bit being input will not be available to the external world on CRUIN.

The functional characteristics of the internal CRU devices are described in the following paragraphs.

Flag Register

Accessible via CRU input and output instructions that are executed to dedicated internal CRU bit addresses (see FIG. 19) is the internal Flag Register 53. The 16-bit Flag Register 53 contains both predefined processor 1 system flags and user-definable flags as detailed in table 3. The predefined system flags are the configuration bit for the Decrementer 51, the Decrementer 51 enable bit, and the internal interrupt request latch CRU inputs 54. Note that CRU output operations to the internal interrupt request latch Flag addresses will not cause these latches to either set or reset. These Flag bits are input only and allow the presence of these interrupt requests to be detected when the occurrence of the interrupts themselves is inhibited by the value of the interrupt mask in the status register 46.

Mid Flag

Accessible via CRU input and output instructions that are executed to a dedicated internal CRU bit address (see FIG. 19) is the MID Flag. The MID Flag is set to one by a MID interrupt, and reset to zero by the software of the MID interrupt routine. Note that setting the MID FLAG to one with a CRU instruction will not cause the MID interrupt to be requested.

External Instructions

The processor 1 has five external instructions (see Table 4) that allow user-defined external functions to be initiated under program control. These instructions are CKON, CKOF, RSET, IDLE, and LREX. Execution of an IDLE instruction causes the processor 1 to enter the idle state and remain in this state until a request occurs for an interrupt level that is not masked by the current value of the interrupt mask in the status register. (Note that the Reset and NMI interrupt levels are not masked by any interrupt mask value.) When any of these five instructions are executed by the processor 1, the processor 1 will use the CRU interface (see FIG. 18) to perform a cycle that is identical to a single-bit CRU output cycle (see FIG. 21) except for the following: (1) the address being output will be non-specific, (2) the data bit being output will be non-specific, (3) a code, specified in Table 4, will be output on D0-D2 to indicate the external instruction being executed. Note that completion of each external instruction and/or generation of Wait states is determined by the READY input.

When the processor 1 is in the idle state, cycles with the idle code will occur repeatedly until a request for an interrupt level that is not masked by the interrupt mask in the status register 46 occurs.

A Hold state can occur during an Idle state, with entry to and return from the Hold state occurring at the IDle code cycle boundaries.

Internal ALU/Other Operation Cycles

When the processor 1 is performing an operation internally and is not using the memory, CRU, or external instruction interfaces or is not in the Hold state, the processor 1 will, for as many CLKOUT cycles as needed, do the following with its interface signals:

1. Output a non-specific address on A0-A14 and A15/CRUOUT

2. Output non-specific data on D0-D7

3. Output logic level high on MEMEN-, DBIN-, and WE-/CRUCLK

4. Output logic level low on IAQ/HOLDA, and

5. Ignore the READY and CRUIN inputs.

The HOLD input is still active, however, as the processor 1 can enter a Hold state while performing an internal ALU/other operation. Also, all interrupt inputs are still active.

Processor Instruction Set

The processor 1 instruction set includes instructions that perform arithmetic, logical, comparison, or manipulation operations on data; loading or storage of internal registers (i.e., program counter, workspace pointer, or status); data transfer between memory and external devices by the CRU; or control functions. The processor 1 instructions contain a variety of available modes for addressing random memory data, e.g., program parameters and flags, or formatted memory data (character strings, data lists, etc.). These addressing modes are Workspace Register Addressing, Workspace Register Indirect Addressing, Workspace Register Indirect Auto Increment Addressing, Symbolic (Direct) Addressing, Indexed Addressing, Immediate Addressing, Program Counter Relative Addressing, CRU Relative Addressing. Workspace Register Addressing means that the Workspace Register contains the actual operand. Workspace Register Indirect Addressing means the Workspace Register contains the address of the operand. Workspace Register Indirect Auto Increment Addressing means that the Workspace Register contains the address of the operand and after the address of the operand is acquired, the contents of the Workspace Register is incremented. Symbolic (Direct) Addressing means the word following the instruction contains the address of the operand. Index addressing means the word following the instruction contains the base address and the Workspace Register contains the index value. The sum of the base address and the index value result in the effective address of the operand. In Immediate Addressing, the word following the instruction contains the operand. Program Counter Relative Addressing means that the 8-bit signed displacement in the right byte (i.e. bits 8 through 15) of the instruction word is multiplyed by two and added to the updated contents of the program counter. This result is placed in the program counter. CRU Relative Addressing means that the 8-bit sign displacement in the right byte of the instruction word is added to the CRU base address (bits 0 through 14 of Workspace Register 12) and the result is the CRU address of the selected CRU bit.

Terminology that will be used to describe the instructions of processor 1 is defined in Table 5. Various processor 1 machine instructions effect the status register. FIG. 5 illustrates the status register bit assignments. Table 7 lists the instructions and their respective effect on the status register.

The following is a list of the individual types of instructions. The dual operand instructions with multiple addressing for source and destination operands have a bit format that is illustrated in FIG. 24a. Note that if B=1, the operands are bytes and the operand addresses are byte addresses. If B=0, the operands are words and the LSB of the operand address is ignored. The addressing mode for each operand is determined by the T field (see Table 7a) of that operand. Table 7b lists the mnemonics for these instructions with the definition of the opcode and a symbolic description.

FIG. 24b illustrates the bit format for dual operand instructions with multiple addressing modes for the source operand and Workspace Register addressing for the destination. The addressing mode for the source operand is determined by the Ts field. (See Table 8a.) Table 8b lists these instructions with the respective opcode and descriptions.

FIG. 24c is a bit format of signed multiply and divide instructions. The addressing modes for the source operand (determined by the Ts field) is shown in Table 9a. The opcode and descriptions of these two instructions is contained in Table 9b.

The extended operation (XOP) instruction bit format is illustrated in FIG. 24d. The Ts and S fields provide multiple mode addressing capability for the source operand. When the XOP is executed, the following transfer occurs (40 hex+4D) is placed in WP. (42 hex+4D) is placed in the program counter. SA (source address) is placed in Workspace Register 11. The old Workspace Pointer (WP) is placed in Workspace Register 13. The old program counter contents is placed in Workspace Register 14. The old status is placed in Workspace Register 15. After these transfers have been made, ST (status bit 6) is set to 1 and ST 7, ST 8, ST 9, ST 10 (overflow interrupt enable), and ST 11 are still set to 0. The processor 1 does not service interrupt trap requests (except for the reset and NMI or nonmaskable interrupt request (at the end of the XOP instruction).

FIG. 24e illustrates the bit format for single operand instructions. The Ts and S fields provide multiple mode addressing capability for the source operand. Table 10 illustrates the opcode for these instructions with a description.

FIG. 24f is a bit map of the CRU multiple-bit instruction. The C field specifies the number of bits to be transferred. If C=0, 16 bits will be transferred. The CRU base register (Workspace Register 12, bits 0 through 14) defines the starting CRU address. The bits are transferred serially and a CRU address is incremented with each bit transfer although the contents of Workspace Register 12 are not effected. Ts and S provide multiple mode addressing capability for the source operand. If eight or fewer bits are transferred, (C=1 through 8), the source address is a byte address. If nine or more bits are transferred (C=0, 9 through 15), the source address is a word address. If the source address is addressed in the Workspace Register indirect auto increment mode, the Workspace Register is incremented by 1 if C=1 through 8, and is incremented by 2 otherwise. If the source is addressed in the register mode, and if the transfer is eight bits or less, bits 8 through 15 are unchanged. Table 11 illustrates these two instructions with their respective opcodes and descriptions.

FIG. 24g is a bit description of the CRU single bit instructions. The sign displacement is added to the contents of Workspace Register 12 (bits 0-14) to form the address of the CRU bit to be selected. Table 12 illustrates these instructions with their respective opcodes and their descriptions.

FIG. 24h illustrates the bit format for the jump instructions. Jump instructions cause the program counter to be loaded with the value selected by program counter relative addressing if the bits of ST (the status) are at specified values. Otherwise no operation occurs and the next instruction is executed since the program counter points to the next instruction. The sign displacement field is a word count to be added to the program counter. Thus, the jump instruction has a range of -128 to 127 words from memory-word address following the jump instruction. No status bits are effected by the jump instruction. Table 13 illustrates the opcode of these jump instructions and the status required to load the program counter, i.e. to jump.

FIG. 24i illustrates the bit format for the shift instructions. If C=0, bits 12 through 15 of Workspace Register 0 contain the shift count. If C=0 and bits 12 through 15 of Workspace Register 0=0 the shift count is 16. Table 14 lists these instructions with their respective opcodes and descriptions.

FIG. 24j illustrates the format for the immediate register instructions. Table 15 lists these instructions with their respective opcodes and descriptions.

FIG. 24k illustrates the bit formats for the Internal Register Load Immediate instructions and these instructions are listed and described in Table 16.

The internal register load and store instructions bit formats are illustrated in FIG. 24l. Table 17 lists these instructions with their respective opcodes and descriptions.

The Return Workspace Pointer instruction (RTWP) bit format is illustrated in FIG. 24m. The RTWP instruction causes the Workspace Register 15 to be loaded into the status register, Workspace Register 14 to be loaded into the program counter and Workspace Register 13 to be loaded into the workspace pointer register.

FIG. 24n illustrates the bit format of the external instructions. The external instructions cause the three data lines (D0-D2) to be set to the levels described in Table 18 and the WE-/CRUCLK- line to be pulsed, allowing external control functions to be initiated. Table 18 also lists these instructions with their respective opcodes and descriptions.

Each of the processor 1 instructions is executed by sequence of machine states (microinstructions) with the length of each sequence depending upon the specific instruction being executed. Each microinstruction is completed in one clock cycle unless wave states are added to a memory or CRU cycle. (Also, each external memory space access of a word in each external CRU cycle requires at least two clock cycles, but will be accomplished with a single microinstruction). The processor 1 incorporates an instruction prefetch scheme which minimizes and in some cases eliminates, the time required to fetch the instruction from memory. Without the prefetch, a typical instruction execution sequence is fetch instruction, decode instruction, fetch source operand if needed, fetch destination operand if needed, process the operands, and store the results if required. The processor 1 makes use of the fact that during the processing of the operands, the memory interface is not required; therefore, the fetch of the next instruction can be accomplished in this time. This instruction is then decoded during the state or states that are required for the results of the previous instruction, which creates more execution overlap. Table 19 illustrates the case of maximum efficiency for an add instruction (instruction opcodes and operands are located in the internal RAM 45). Note that it effectively takes only four machine cycles to peform all six steps.

                  TABLE 1                                                          ______________________________________                                         REG-                                                                           ISTER                                                                          NO.    CONTENTS     USED DURING                                                ______________________________________                                          0     Shift count  Shift instructions (SLA, SRA,                                     (optional)   SRC, and SLC)                                                     Multiplicand and                                                                            Signed Multiply                                                   MSW of result                                                                  MSW of dividend                                                                             Signed Divide                                                     and quotient                                                             1     LSW of result                                                                               Signed Multiply                                                   LSW of dividend                                                                             Signed Divide                                                     and remainder                                                           11     Return Address                                                                              Branch and Link Instruction (BL)                                  Effective Address                                                                           Extended Operation (XOP)                                   12     CRU Base     CRU instructions (SBO, SBZ, TB,                                   Address      LDCR, and STCR)                                            13     Saved WP     Context switching (BLWP, RTWP,                                    register     XOP, interrupts)                                           14     Saved PC register                                                                           Context switching (BLWP, RTWP,                                                 XOP, interrupts)                                           15     Saved ST register                                                                           Context switching (BLWP, RTWP,                                                 XOP, interrupts)                                           ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________                VECTOR MASK VALUES                                                             LOCATION                                                                              TO ENABLE MASK VALUE                                         PRIORITY   (Memory                                                                               ACCEPTING AFTER TAKING                                       LEVELS     Address,                                                                              THE INTERRUPT                                                                            THE INTERRUPT                                                                            SOURCE AND                               (In Order of Priority)                                                                    In Hex)                                                                               (ST12 THRU ST15)                                                                         (ST12 THRU ST15)                                                                         ASSIGNMENT                               __________________________________________________________________________     0 (Highest Priority)                                                                      0000   0.sub.16 thru F.sub.16                                                                   0000                                                                                      ##STR1##                                MID        0008   0.sub.16 thru F.sub.16                                                                   0001      Internal: MID                            NMI        FFFC   0.sub.16 thru F.sub.16                                                                   0000                                                                                      ##STR2##                                1          0004   1.sub.16 thru F.sub.16                                                                   0000                                                                                      ##STR3##                                2          0008   2.sub.16 thru F.sub.16                                                                   0001      Internal:                                                                      Arithmetic Overflow                      3          000C   3.sub.16 thru F.sub.16                                                                   0002      Internal:                                                                      Decrementer                              4          0010   4.sub.16 thru F.sub.16                                                                   0003      External: User-                                                                defined                                  __________________________________________________________________________

                  TABLE 3                                                          ______________________________________                                                CRU BIT                                                                 BIT    ADDRESS.sup.+                                                                             DESCRIPTION                                                  ______________________________________                                         FLAG0  1EE0       Set to 0: Decrementer configured as                                                      Interval Timer.                                                      Set to 1: Decrementer configured as                                                      Event Counter.                                     FLAG1  1EE2       Set to 0: Decrementer not enabled                                              Set to 1: Decrementer enabled (will                                                      decrement and can set in-                                                      ternal latch that requests a                                                   level 3 interrupt).                                FLAG2  1EE4       Level 1 Internal Interrupt Request                                             Latch CRU Input (Input-only).                                                  0: Level 1 request not present                                                 1: Level 1 request present                                   FLAG3  1EE6       Level 3 Internal Interrupt Request                                             Latch CRU Input (Input-only).                                                  0: Level 3 request not present                                                 1: Level 3 request present                                   FLAG4  1EE8       Level 4 Internal Interrupt Request                                             Latch CRU Input (Input-only).                                                  0: Level 4 request not present                                                 1: Level 4 request present                                   FLAG5  1EEA       User Defined                                                 FLAG6  1EEC                                                                    FLAG7  1EEE                                                                    FLAG8  1EF0                                                                    FLAG9  1EF2                                                                    FLAGA  1EF4                                                                    FLAGB  1EF6                                                                    FLAGC  1EF8                                                                    FLAGD  1EFA                                                                    FLAGE  1EFC                                                                    FLAGF  1EFE                                                                    ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                                     CODE DURING CYCLE                                                  INSTRUCTION   D0           D1    D2                                            ______________________________________                                         CRU:                                                                           SBO, SBZ, TB, 0            0     0                                             LDCR or STCR                                                                   IDLE          0            1     0                                             RSET          0            1     1                                             CKON          1            0     1                                             CKOF          1            1     0                                             LREX          1            1     1                                             ______________________________________                                    

                  TABLE 5                                                          ______________________________________                                         TERM      DEFINITIONS                                                          ______________________________________                                         B         Byte Indicator (1 = byte; 0 = word)                                  C         Bit Count                                                            D         Destination address register                                         DA        Destination address                                                  IOP       Immediate operand                                                    LSB (n)   Least-significant (right most) bit of (n)                            MSB (n)   Most-significant (left most) bit of (n)                              N         Don't care                                                           PC        Program Counter                                                      Result    Result of operation performed by instruction                         S         Source address register                                              SA        Source address                                                       ST        Status register                                                      STn       Bit n of status register                                             TD        Destination address modifier                                         TS        Source address modifier                                              W         Workspace register                                                   WRn       Workspace register n                                                 (n)       Contents of n                                                        a → b                                                                             a is transferred to b -|n| Absolute value of                 n                                                                    +         Arithmetic addition                                                  -         Arithmetic subtraction                                               AND       Logical AND                                                          OR        Logical OR                                                           ⊕     Logical exclusive OR                                                  -n       Logical complement of n                                              ·                                                                               Arithmetic multiplication                                            ______________________________________                                    

                                      TABLE 6a                                     __________________________________________________________________________                         CONDITION TO SET BIT TO 1, OTHERWISE                                INSTRUCTION                                                                               SET TO 0 FOR INSTRUCTION LISTED.                                    AND/OR     ALSO, THE EFFECT OF OTHER                                  BIT                                                                               NAME  INTERRUPT  INSTRUCTIONS AND INTERRUPTS                                __________________________________________________________________________     ST0                                                                               Logical                                                                              C, CB      If MSB (SA) = 1 and MSB (DA) = 0, or                          Greater          If MSB (SA) = MSB (DA) and MSB of                             Than             [(DA) - (SA)] = 1.                                                  CI         If MSB (W) = 1 and MSB of IOP = 0, or                                          If MSB (W) = MSB of IOP and MSB of                                             [IOP - (W)] = 1.                                                    ABS, LDCR  If (SA) ≠ 0                                                   RTWP       If bit (0) of WR15 is 1                                             LST        If bit (0) of selected WR is 1                                      A, AB, AI, ANDI,                                                                          If result ≠ 0                                                 DEC, DECT, LI,                                                                 MOV, MOVB, NEG,                                                                ORI, S, SB,                                                                    DIVS, MPYS, INC,                                                               INCT, INV, SLA,                                                                SOC, SOCB, SRA,                                                                SRC, SRL, STCR,                                                                SZC, SZCB, XOR                                                                 Reset Interrupt                                                                           Unconditionally sets status bit to 0                                All other instructions                                                                    Do not affect the status bit (see Note 1)                           and interrupts                                                        ST1                                                                               Arithmetic                                                                           C, CB      If MSB (SA) = 0 and MSB (DA) = 1, or                          Greater          If MSB (SA) = MSB (DA) and MSB of                             Than             [(DA) - (SA)] = 1.                                                  CI         If MSB (W) = 0 and MSB of IOP = 1, or                                          If MSB (W) = MSB of IOP and MSB of                                             [IOP - (W)] = 1.                                                    ABS, LDCR  If MSB (SA) = 0 and (SA) ≠ 0                                  RTWP       If bit (1) of WR15 is 1                                             LST        If bit (1) of selected WR is 1                                      A, AB, AI, ANDI,                                                                          If MSB of result = 0 and result ≠ 0                           DEC, DECT, LI,                                                                 MOV, MOVB, NEG,                                                                ORI, S, SB, DIVS,                                                              MPYS, INC, INCT,                                                               INV, SLA, SOC,                                                                 SOCB, SRA, SRC,                                                                SRL, STCR, SZC,                                                                SZCB, XOR                                                                      Reset Interrupt                                                                           Unconditionally sets status bit to 0                                All other instructions                                                                    Do not affect the status bit                                        and interrupts                                                        __________________________________________________________________________

                                      TABLE 6b                                     __________________________________________________________________________                         CONDITION TO SET BIT TO 1, OTHERWISE                                INSTRUCTION                                                                               SET TO 0 FOR INSTRUCTION LISTED.                                    AND/OR     ALSO, THE EFFECT OF OTHER                                  BIT                                                                               NAME  INTERRUPT  INSTRUCTIONS AND INTERRUPTS                                __________________________________________________________________________     ST2                                                                               Equal C, CB      If (SA) = (DA)                                                      CI         If (W) = IOP                                                        COC                                                                                        ##STR4##                                                           CZC        If (SA) and (DA) = 0                                                TB         If CRUIN = 1 for addressed CRU bit                                  ABS, LDCR  If (SA) = 0                                                         RTWP       If bit (2) of WR15 is 1                                             LST        If bit (2) of selected WR is 1                                      A, AB, AI, ANDI,                                                                          If result = 0                                                       DEC, DECT, LI,                                                                 MOV, MOVB, NEG,                                                                ORI, S, SB, DIVS,                                                              MPYS, INC, INCT,                                                               INV, SLA, SOC,                                                                 SOCB, SRA, SRC,                                                                SRL, STCR, SZC,                                                                SZCB, XOR                                                                      Reset Interrupt                                                                           Unconditionally sets status bit to 0                                All other instructions                                                                    Do not affect the status bit (see Note 1)                           and interrupts                                                        ST3                                                                               Carry A, AB, ABS, AI,                                                                           If CARRY OUT = 1                                                    DEC, DECT, INC,                                                                INCT, NEG, S, SB                                                               SLA, SRA, SRL,                                                                            If last bit shifted out = 1                                         SRC                                                                            RTWP       If bit (3) of WT15 is 1                                             LST        If bit (3) of selected WR is 1                                      Reset Interrupt                                                                           Unconditionally sets status bit to 0                                All other instructions                                                                    Do not affect the status bit (see Note 1)                           and interrupts                                                        ST4                                                                               Overflow                                                                             A, AB      If MSB (SA) = MSB (DA) and MSB                                                 of result ≠ MSB (DA)                                          AI         If MSB (W) = MSB of IOP and MSB                                                of result ≠ MSB (W)                                           S, SB      If MSB (SA) ≠ MSB (DA) and MSB                                           of result ≠ MSB (DA)                                          DEC, DECT  If MSB (SA) = 1 and MSB of result = 0                               INC, INCT  If MSB (SA) = 0 and MSB of result =  0                              SLA        If MSB changes during shift                                         DIV        If MSB (SA) = 0 and MSB (DA) = 1, or if                                        MSB (SA) = MSB (DA) and MSB of                                                 [(DA) - (SA)] = 0                                                   DIVS       If the quotient cannot be expressed as a                                       signed 16 bit quanity (8000.sub.16 is a valid                                  negative number)                                                    ABS, NEG   If (SA) = 8000.sub.16                                               RTWP       If bit (4) of WR15 is 1                                             LST        If bit (4) of selected WR is 1                                      Reset Interrupt                                                                           Unconditionally sets status bit to 0                                All other instructions                                                                    Do not affect the status bit (see Note 1)                           and interrupts                                                        __________________________________________________________________________

                                      TABLE 6c                                     __________________________________________________________________________                         CONDITION TO SET BIT TO 1, OTHERWISE                                INSTRUCTION                                                                               SET TO 0 FOR INSTRUCTION LISTED.                                    AND/OR     ALSO, THE EFFECT OF OTHER                                  BIT                                                                               NAME  INTERRUPT  INSTRUCTIONS AND INTERRUPTS                                __________________________________________________________________________     ST5                                                                               Odd   CB, MOVB   If (SA) has odd number of 1's                                 Parity                                                                               LDCR       If ≦ C ≦ 8 and (SA) has odd number of                            1's.                                                                           If C = 0 or 9 ≦ C ≦ 15, does not affect                          the                                                                            status bit.                                                         STCR       If 1 ≦ C ≦ 8 and the stored bits have                            an odd                                                                         number of 1's. If C = 0 or 9 ≦ C ≦ 15,                           does                                                                           not affect the status bit.                                          AB, SB, SOCB,                                                                             If result has odd number of 1's.                                    SZCB                                                                           RTWP       If bit (5) of WT15 is 1                                             LST        If bit (5) of selected WR is 1                                      Reset Interrupt                                                                           Unconditionally sets status bit to 0                                All other instructions                                                                    Do not affect the status bit (see Note 1)                           and Interrupts                                                        ST6                                                                               XOP   XOP        If XOP instruction is executed                                      RTWP       If bit (6) of WR15 is 1                                             LST        If bit (6) of selected WR is 1                                      Reset Interrupt                                                                           Unconditionally sets status bit to 0                                All other instructions                                                                    Do not affect the status bit (see Note 1)                           and interrupts                                                        ST7                                                                               Unused                                                                               RTWP       If corresponding bit of WR15 is 1                          ST8                                                                               Bits  LST        If corresponding bit of selected WR is 1.                  ST9      XOP, Any   Unconditionally sets each of these status                  and      Interrupt  bits to 0                                                  ST11     All other instructions                                                                    Do not affect these status bits (see Note 1)               ST10                                                                              Arithmetic                                                                           RTWP       If bit (10) of WR is 1                                        Overflow                                                                             LST        If bit (10) of selected WR is 1                               Enable                                                                               XOP, Any   Unconditionally sets status bit to 0                                Interrupt                                                                      All other instructions                                                                    Do not affect the status bit (see Note 1)                  ST12                                                                              Interrupt                                                                            LIMI       If corresponding bit of IOP is 1                           ST13                                                                              Mask  RTWP       If corresponding bit of WR15 is 1                          ST14     LST        If corresponding bit of selected WR is 1.                  and      RST, Reset and                                                                            Unconditionally sets each of these status                  ST15     NMI Interrupts                                                                            bits to 0                                                           All other interrupts                                                                      If ST12 - ST15 = 0, no change                                                  If ST12 = ST15 ≠ 0, set to one                                           Less than level of the interrupt trap taken                         All other instructions                                                                    Do not affect these status bits (see Note                  __________________________________________________________________________                         1)                                                    

                  TABLE 7a                                                         ______________________________________                                         T.sub.S or T.sub.D                                                                    S or D     ADDRESSING MODE   NOTES                                      ______________________________________                                         00     0, 1 . . . 15                                                                             Workspace register                                                                               1                                          01     0, 1 . . . 15                                                                             Workspace register indirect                                  10     0          Symbolic          4                                          10     1, 2 . . . 15                                                                             Indexed           2, 4                                       11     0, 1 . . . 15                                                                             Workspace register indirect                                                                      3                                                            auto increment                                               ______________________________________                                          NOTES:                                                                         1 When a workspace register is the operand of a byte instruction (bit 3 =      1), the left byte (bits 0 through 7) is the operand and the right byte         (bits 8 through 15) is unchanged.                                              2 Workspace register 0 may not be used for indexing.                           3 The workspace register is incremented by 1 for byte instructions (bit 3      = 1) and is incremented by 2 for word instructions (bit 3 = 0).                4 When T.sub.S = T.sub.D = 10, two words are required in addition to the       instruction word. The first word is the source operand base address and        the second word is the destination operand base address.                 

                                      TABLE 7b                                     __________________________________________________________________________                                      RESULT  STATUS                                        OP CODE                                                                               B                 COMPARED                                                                               BITS                                  MNEMONIC                                                                               0 1  2 3  MEANING        TO 0    AFFECTED                                                                              DESCRIPTION                    __________________________________________________________________________     A       1 0  1 0  Add            Yes     0-4    (SA) + (DA) →                                                           (DA)                           AB      1 0  1 1  Add bytes      Yes     0-5    (SA) + (DA) →                                                           (DA)                           C       1 0  0 0  Compare        No      0-2    Compare (SA) to (DA) and                                                       set                                                                            appropriate status bits        CB      1 0  0 1  Compare bytes  No      0-2,5  Compare (SA) to (DA) and                                                       set                                                                            appropriate status bits        S       0 1  1 0  Subtract       Yes     0-4    (DA) - (SA) →                                                           (DA)                           SB      0 1  1 1  Subtract bytes Yes     0-5    (DA) - (SA) →                                                           (DA)                           SOC     1 1  1 0  Set ones corresponding                                                                        Yes     0-2    (DA) OR (SA) →                                                          (DA)                           SOCB    1 1  1 1  Set ones corresponding bytes                                                                  Yes     0- 2,5 (DA) OR (SA) →                                                          (DA)                           SZC     0 1  0 0  Set zeroes corresponding                                                                      Yes     0-2                                                                                    ##STR5##                      SZCB    0 1  0 1  Set zeroes corresponding bytes                                                                Yes     0-2,5                                                                                  ##STR6##                      MOV     1 1  0 0  Move           Yes     0-2    (SA) → (DA)             MOVB    1 1  0 1  Move bytes     Yes     0-2,5  (SA) → (DA)             __________________________________________________________________________

                  TABLE 8a                                                         ______________________________________                                         T.sub.S                                                                            S           ADDRESSING MODE     NOTES                                      ______________________________________                                         00  0, 1 . . . 15                                                                              Workspace register                                             01  0, 1 . . . 15                                                                              Workspace register indirect                                    10  0           Symbolic                                                       10  1, 2 . . . 15                                                                              Indexed             1                                          11  0, 1 . . . 15                                                                              Workspace register indirect auto                                                                   2                                                          increment                                                      ______________________________________                                          NOTES:                                                                         1 Workspace register 0 may not be used for indexing.                           2 The workspace register is incremented by 2.                            

                                      TABLE 8b                                     __________________________________________________________________________                              RESULT  STATUS                                        MNE- OP CODE             COMPARED                                                                               BITS AF-                                      MONIC                                                                               0 1 2 3 4 5 MEANING TO 0    FECTED                                                                               DESCRIPTION                             __________________________________________________________________________     COC  0 0 1 0 0 0 Compare ones                                                                           No      2     Test (D) to determine if 1's are                                               in each bit                                              corresponding         position where 1's are in (SA). If                                             so, set ST2.                            CZC  0 0 1 0 0 1 Compare zeroes                                                                         No      2     Test (D) to determine if 0's are                                               in each bit                                              corresponding         position where 1's are in (SA). If                                             so, set ST2.                            XOR  0 0 1 0 1 0 Exclusive OR                                                                           Yes     0-2   (DA) ⊕ (SA) → (D)            MPY  0 0 1 1 1 0 Multiply                                                                               No      --    Multiply unsigned (D) by unsigned                                              (SA) and                                                                       place unsigned 32-bit product in D                                             (most-                                                                         significant) and D+1                                                           (least-significant). If WR15                                                   is D, the next word in memory                                                  after WR15 will                                                                be used for the least significant                                              half of the                                                                    product.                                DIV  0 0 1 1 1 1 Divide  No      4     If unsigned (SA) is less than or                                               equal to unsigned                                                              (D), perform no operation and set                                              ST4. Otherwise                                                                 divide unsigned (D) and (D+1) by                                               unsigned (SA).                                                                 Quotient → (D), remainder                                               → (D+1). If D = 15,                                                     the next word in memory after WR15                                             will be                                                                        used for the remainder.                 __________________________________________________________________________

                  TABLE 9a                                                         ______________________________________                                         T.sub.S                                                                            S           ADDRESSING MODE   NOTES                                        ______________________________________                                         00  0, 1 . . . 15                                                                              Workspace register                                                                               1                                            01  0, 1 . . . 15                                                                              Workspace register indirect                                                                      1                                            10  0           Symbolic          1                                            10  1, 2 . . . 15                                                                              Indexed           1,2                                          11  0, 1 . . . 15                                                                              Workspace register indirect                                                                      1,3                                                          auto increment                                                 ______________________________________                                          NOTES:                                                                         1 Workspace registers 0 and 1 contain operands used in the signed multipl      and divide operations.                                                         2 Workspace register 0 may not be used for indexing.                           3 The workspace register is incremented by 2.                            

                                      TABLE 9b                                     __________________________________________________________________________                                     RESULT  STATUS                                 MNE- OP CODE                    COMPARED                                                                               BITS                                   MONIC                                                                               0 1 2 3 4 5 6 7 8 9 MEANING                                                                               TO 0    AFFECTED                                                                              DESCRIPTION                     __________________________________________________________________________     MPYS 0 0 0 0 0 0 0 1 1 1 Signed Yes     0-2    Multiply signed two's                                                          com-                                                     Multiply              plement integer in WR0 by                                                      signed two's complement                                                        integer (SA) and place                                                         signed                                                                         32-bit product in WR0                                                          (most-                                                                         significant) and WR1                                                           least-                                                                         significant.                    DIVS 0 0 0 0 0 0 0 1 1 0 Signed Yes     0-2,4  If the quotient cannot be                                                      ex-                                                      Divide                pressed as a signed 16                                                         bit                                                                            quantity (8000 (hex) is a                                                      valid                                                                          negative number), set                                                          ST4.                                                                           Otherwise, divide signed,                                                      two's                                                                          complement integer in WR0                                                      and WR1 by the signed                                                          two's                                                                          complement integer (SA)                                                        and                                                                            place the signed quotient                                                      in                                                                             WR0 and the signed                                                             remainder                                                                      in WR1. The sign of the                                                        quo-                                                                           tient is determined by                                                         algebraic                                                                      rules. The sign of the                                                         remainder                                                                      is the same as the sign of                                                     the                                                                            dividend and                                                                   |REMAINDER.vertlin                                                    e.                                                                             < |DIVISOR.vertlin                                                    e.                              __________________________________________________________________________

                                      TABLE 10                                     __________________________________________________________________________                                     RESULT  STATUS                                 MNE- OP CODE                    COMPARED                                                                               BITS AF-                               MONIC                                                                               0 1 2 3 4 5 6 7 8 9 MEANING                                                                               TO ZERO FECTED                                                                               DESCRIPTION                      __________________________________________________________________________     B    0 0 0 0 0 1 0 0 0 1 Branch No      --    SA → (PC)                 BL   0 0 0 0 0 1 1 0 1 0 Branch No      --    (PC) → (WR11); SA                                                       → (PC)                                             and link                                              BLWP 0 0 0 0 0 1 0 0 0 0 Branch No      --    (SA) → (WP); (SA +                                                      2) → (PC);                                         and load             (old WP) → (new                                                         WR13);                                                    workspace            (old PC) → (new                                                         WR14);                                                    pointer              (old ST) → (new                                                         WR15);                                                                         The TMS 9995 does not ser-                                                     vice interrupt trap                                                            requests                                                                       (except for the Reset and                                                      NMI                                                                            Requests) at the end of                                                        the                                                                            BLWP instruction.                CLR  0 0 0 0 0 1 0 0 1 1 Clear  No      --    0 → (SA)                                           Operand                                               SETO 0 0 0 0 0 1 1 1 0 0 Set to No      --    FFFF.sub.16 → (SA)                                 ones                                                  INV  0 0 0 0 0 1 0 1 0 1 Invert Yes     0-2                                                                                   ##STR7##                        NEG  0 0 0 0 0 1 0 1 0 0 Negate Yes     0-4   -(SA) → (SA)              ABS  0 0 0 0 0 1 1 1 0 1 Absolute                                                                              No      0-4   |(SA)|                                                       → (SA)                                             value*                                                SWPB 0 0 0 0 0 1 1 0 1 1 Swap   No      --    (SA), bits 0 thru 7                                                            → (SA)                                             bytes                bits 8 thru 15; (SA),                                                          bits 8 thru 15 →                                                        (SA),                                                                          bits 0 thru 7.                   INC  0 0 0 0 0 1 0 1 1 0 Increment                                                                             Yes     0-4   (SA) + 1 → (SA)           INCT 0 0 0 0 0 1 0 1 1 1 Increment                                                                             Yes     0-4   (SA) + 2 → (SA)                                    by two                                                DEC  0 0 0 0 0 1 1 0 0 0 Decrement                                                                             Yes     0- 4  (SA) - 1 → (SA)           DECT 0 0 0 0 0 1 1 0 0 1 Decrement                                                                             Yes     0-4   (SA) - 2 → (SA)                                    by two                                                X**  0 0 0 0 0 1 0 0 1 0 Execute                                                                               No      --    Execute the instruction                                                        at SA.                           __________________________________________________________________________      *Operand is compared to zero for status bit.                                   **If additional memory words for the execute instruction are required to       define the operands of the instruction located at SA, these words will be      accessed from PC and the PC will be updated accordingly. The instruction       acquisition signal (IAQ) will not be true when the TMS 9995 accesses the       instruction at SA. Status bits are affected in the normal manner for the       instruction executed.                                                    

                                      TABLE 11                                     __________________________________________________________________________                                 RESULT  STATUS                                             OP CODE             COMPARED                                                                               BITS                                       MNEMONIC                                                                               0 1 2 3 4 5 MEANING TO 0    AFFECTED                                                                              DESCRIPTION                         __________________________________________________________________________     LDCR    0 0 1 1 0 0 Load    Yes     0-2,5  Beginning with                                          communication          LSB of (SA),                                            register               transfer the                                                                   specified number                                                               of bits from (SA)                                                              to the CRU.                         STCR    0 0 1 1 0 1 Store   Yes     0-2,5  Beginning with                                          communication          LSB of (SA),                                            register               transfer the                                                                   specified number                                                               of bits from the                                                               CRU to (SA)                                                                    Load unfilled bit                                                              positions with                      __________________________________________________________________________                                                0.                             

                                      TABLE 12                                     __________________________________________________________________________                                    STATUS                                                  OP CODE                BITS                                            MNEMONIC                                                                               0 1 2 3 4 5 6 7 MEANING                                                                               AFFECTED                                                                              DESCRIPTION                              __________________________________________________________________________     SBO     0 0 0 1 1 1 0 1 Set bit to                                                                            --     Set the selected                                                 one           output bit to 1.                         SBZ     0 0 0 1 1 1 1 0 Set bit to                                                                            --     Set the selected                                                 zero          output bit to 0.                         TB      0 0 0 1 1 1 1 1 Test bit                                                                              2      If the selected                                                                CRU input bit =                                                                1, set ST2; if the                                                             selected CRU in-                                                               put = 0, set ST2                                                               = 0.                                     __________________________________________________________________________

                                      TABLE 13                                     __________________________________________________________________________             OP CODE                                                                MNEMONIC                                                                               0 1 2 3 4 5 6 7 MEANING   ST CONDITION TO LOAD PC                      __________________________________________________________________________     JEQ     0 0 0 1 0 0 1 1 Jump equal                                                                               ST2 = 1                                      JGT     0 0 0 1 0 1 0 1 Jump greater than                                                                        ST1 = 1                                      JH      0 0 0 1 1 0 1 1 Jump high ST0 = 1 and ST2 = 0                          JHE     0 0 0 1 0 1 0 0 Jump high or equal                                                                       ST0 = 1 or ST2 = 1                           JL      0 0 0 1 1 0 1 0 Jump low  ST0 = 0 and ST2 = 0                          JLE     0 0 0 1 0 0 1 0 Jump low or equal                                                                        ST0 = 0 or ST2 = 1                           JLT     0 0 0 1 0 0 0 1 Jump less than                                                                           ST1 = 0 and ST2 = 0                          JMP     0 0 0 1 0 0 0 0 Jump unconditional                                                                       Unconditional                                JNC     0 0 0 1 0 1 1 1 Jump no carry                                                                            ST3 = 0                                      JNE     0 0 0 1 0 1 1 0 Jump not equal                                                                           ST2 = 0                                      JNO     0 0 0 1 1 0 0 1 Jump no overflow                                                                         ST4 = 0                                      JOC     0 0 0 1 1 0 0 0 Jump on carry                                                                            ST3 = 1                                      JOP     0 0 0 1 1 1 0 0 Jump odd parity                                                                          ST5 = 1                                      __________________________________________________________________________

                                      TABLE 14                                     __________________________________________________________________________                                    RESULT  STATUS                                          OP CODE                COMPARED                                                                               BITS                                    MNEMONIC                                                                               0 1 2 3 4 5 6 7 MEANING                                                                               TO 0    AFFECTED                                                                              DESCRIPTION                      __________________________________________________________________________     SLA     0 0 0 0 1 0 1 0 Shift left                                                                            Yes     0-4    Shift (W) left.                                          arithmetic            Fill vacated                                                                   bit positions                                                                  with 0.                          SRA     0 0 0 0 1 0 0 0 Shift right                                                                           Yes     0-3    Shift (W) right.                                         arithmetic            Fill vacated bit                                                               positions with                                                                 original MSB                                                                   of (W).                          SRC     0 0 0 0 1 0 1 1 Shift right                                                                           Yes     0-3    Shift (W) right.                                         circular              Shift previous                                                                 LSB into MSB.                    SRL     0 0 0 0 1 0 0 1 Shift right                                                                           Yes     0-3    Shift (W) right.                                         logical               Fill vacated bit                                                               positions with                                                                 0's.                             __________________________________________________________________________

                                      TABLE 15                                     __________________________________________________________________________                                         RESULT  STATUS                             MNE-  OP CODE                       COMPARED                                                                               BITS                               MONIC 0 1 2 3 4 5 6 7 8 9 10                                                                               MEANING TO 0    AFFECTED                                                                              DESCRIPTION                 __________________________________________________________________________     AI    0 0 0 0 0 0 1 0 0 0 1 Add immediate                                                                          Yes     0-4    (W) + IOP →                                                             (W)                         ANDI  0 0 0 0 0 0 1 0 0 1 0 AND immediate                                                                          Yes     0-2    (W) AND IOP →                                                           (W)                         CI    0 0 0 0 0 0 1 0 1 0 0 Compare imme-                                                                          Yes     0-2    Compare (W) to                                          diate                  IOP and set appro-                                                             priate status bits.         LI    0 0 0 0 0 0 1 0 0 0 0 Load immediate                                                                         Yes     0-2    IOP → (W)            ORI   0 0 0 0 0 0 1 0 0 1 1 OR immediate                                                                           Yes     0-2    (W) OR IOP →         __________________________________________________________________________                                                        (W)                    

                                      TABLE 16                                     __________________________________________________________________________             OP CODE                                                                MNEMONIC                                                                               0 1 2 3 4 5 6 7 8 9 10                                                                               MEANING  DESCRIPTION                             __________________________________________________________________________     LWPI    0 0 0 0 0 0 1 0 1 1 1 Load workspace                                                                          IOP → (WP), no ST bits                                         pointer immediate                                                                       affected.                               LIMI    0 0 0 0 0 0 1 1 0 0 0 Load interrupt                                                                          IOP, bits 12 thru 15 →                                         mask     ST12 thru ST15.                         __________________________________________________________________________

                                      TABLE 17                                     __________________________________________________________________________                                            STATUS                                          OP CODE                        BITS                                    MNEMONIC                                                                               0 1 2 3 4 5 6 7 8 9 10                                                                               11                                                                               MEANING                                                                               AFFECTED                                                                              DESCRIPTION                      __________________________________________________________________________     STST    0 0 0 0 0 0 1 0 1 1 0 0 Store status                                                                          --     (ST) → (W)                                                Register                                       LST     0 0 0 0 0 0 0 0 1 0 0 0 Load status                                                                           0-15   (W) → (ST)                                                Register                                       STWP    0 0 0 0 0 0 1 0 1 0 1 0 Store work-                                                                           --     (WP) → (W)                                                space pointer                                  LWP     0 0 0 0 0 0 0 0 1 0 0 1 Load work-                                                                            --     (W) → (WP)                                                space pointer                                  __________________________________________________________________________

                                      TABLE 18                                     __________________________________________________________________________                                             STATUS                                         OP CODE                         BITS             DATA BUS              MNEMONIC                                                                               0 1  2 3  4 5  6 7 8 9 10                                                                               MEANING                                                                               AFFECTED                                                                              DESCRIPTION                                                                              D0                                                                               D1                                                                               D2                __________________________________________________________________________     IDLE    0 0  0 0  0 0  1 1 0 1 0 Idle   --     Suspend TMS                                                                              L995                                                                             H L                                                                instruction execution                                                          until an unmasked                                                              interrupt level                                                                request occurs.                 RSET    0 0  0 0  0 0  1 1 0 1 1 Reset  12-15  Set ST12-ST15                                                                            L H H                                                                to zero.                        CKOF    0 0  0 0  0 0  1 1 1 1 0 User defined                                                                          --     --        H H L                 CKON    0 0  0 0  0 0  1 1 1 0 1 User defined                                                                          --     --        H L H                 LREX    0 0  0 0  0 0  1 1 1 1 1 User defined                                                                          --     --        H H H                 __________________________________________________________________________

                  TABLE 19                                                         ______________________________________                                               STATE    MEMORY                                                          STEP  COUNT    CYCLE        INTERNAL FUNCTION                                  ______________________________________                                         1              Fetch Instruction                                                                           Process Previous                                                               Operands                                           2     1        Write Results                                                                               Decode Instruction                                 3     2        Fetch Source                                                    4     3        Fetch Destination                                               5     4        Fetch Next   Add                                                               Instruction                                                     6              Write Results                                                                               Decode Instruction                                 ______________________________________                                     

What we claim is:
 1. A digital processing system of a plurality of semiconductor substrates comprising:an external memory means for storing instructions of a first structure, said external memory means fabricated on at least one semiconductor substrate; a processor unit fabricated on a semiconductor substrate and connected to said external memory means, said processor unit further comprising: internal memory means for the storage of data of a second structure; arithmetic and logic means for performing operations on said data; register means for temporarily storing said data and addresses for accessing said internal and said external memory means; a first information path of said first structure for connecting said internal memory means, to said arithmetic and logic means via said register means; a second information path of said second structure for connecting said external memory to said first information path; multiplexer means for multiplexing said first information path and the second information path to the register means; and control and timing circuits for the execution of said instructions for accessing the internal memory means, said external memory means and said register means and for controlling said operations on said data by said arithmetic and logic means.
 2. A digital processing system according to claim 1, wherein said second structure comprises 16 bit addresses and 16 bit instruction.
 3. A digital processing system according to claim 1, wherein said first structure comprises 16 bit addresses and 8 bit data.
 4. A digital processing system according to claim 1, wherein said processor unit includes external memory interface means to receive instructions from the external memory via said second information path for application to said first information path.
 5. A digital processing system comprising:an external program memory means for storing of a plurality of programs; each program containing a plurality of instructions of a first structure, said external program memory means being fabricated on at least one semiconductor substrate; a processor unit fabricated on a semiconductor substrate and connected to said external program memory means via a bus of said first structure, said processor unit comprising: internal memory means for storing data of second structure and addresses for accessing said programs in said external memory; arithmetic and logic means for performing operations on said data; register means for temporary storage of said data and said addresses; a first path of a second structure for connecting said internal memory means to said arithmetic and logic means via said register means; control and timing circuit means for execution of said instructions for accessing the internal memory means, said external program memory means and said register means and for controlling said operations on said data by said arithmetic and logic means.
 6. A digital processing system according to claim 5, wherein said second structure includes 16 bit addresses and 16 bit instructions.
 7. A digital processing system according to claim 5, wherein said first structure includes 16 bit addresses and 8 bit data.
 8. A digital processing system according to claim 5, wherein said processor unit includes external memory interface means to receive instructions from said external program memory means via said bus for application to said first path.
 9. A digital processing system of a plurality of semiconductor substrates comprising:an external memory means for storing instructions of a second structure; a processor unit fabricated on a semiconductor substrate and connected to said external memory means, said processor unit further comprising: internal memory means for storage of data or instructions; arithmetic and logic means for performing operations on said instructions; register means for temporarily storing of said data and addresses for accessing said internal memory means and said external memory; a first path of said first structure for connecting said internal memory means to said arithmetic and logic means via said register means; a second data path of a second structure for connecting said external memory to said first path; multiplexer means for multiplexing the first path and the second data path to the register means; and control and timing circuit means for executing said instructions and for accessing said internal memory means, said external memory means, and said register means and for controlling said operations on said data by said arithmetic and logic means.
 10. A digital processing system according to claim 9, wherein said first structure includes 16 bit addresses and 16 bit instructions.
 11. A digital processing system according to claim 9 wherein said second structure includes 16 bit addresses and 8 bit data.
 12. A digital processing system according to claim 9, wherein said processor unit includes an external memory interface means to receive instructions from said external memory via said second path for application to said first path. 